Not sure how long it will last with Ryanair starting 4 weekly service and there is Blue Air's 3 weekly service to.
Blue Air haven't long left, so a good move by TAROM to get them off the route to cosy up next to Ryanair ~ I understand a lot of connecting traffic thanks to SkyTeam partners for them as well as Romanians going to/from Bucharest and within Romania.
Probably won`t be too long before Dublin-Sofia services are relaunched.
I could see it being re-introduced for Winter operations by Aer Lingus, it done well back in Winter 2008/2009 with Topflight using some seats, didn't do well in the Summer months, and Aer Lingus preferred to use there aircraft elsewhere wisely.